# Python Functools Partial Function

Functools are the standard framework used in Python when working with high-order functions that act on or return other functions, and it helps to extend or use the functions without rewriting them. Using Functools makes the code readable and easy maintenance with high efficiency.

This library contains two main functions: `partial`

and `partialmethod`

. The `partialmethod`

is a non-callable method descriptor of an already defined function for specific arguments and returns a new `partialmethod`

descriptor.

Let’s have a look at the `partial()`

function.

## Use the Functools `partial()`

Function in Python

The `partial()`

function is a higher-order function that takes a function as input and returns a function that can use in a program like other functions. When there is a function with lots of arguments, but we need to change only one or two arguments every time we use that function, the `partial()`

function, which comes along with the Functools library, aids in such situations.

With the help of the `partial()`

function, we can freeze a specific number of arguments from a function and create a new simplified one to return a new `partial()`

object with positional arguments and keywords. Therefore, it prevents us from rewriting the original function.

Overall, `partial()`

is a handy tool, especially in applying various inputs to a single object or wrapping one of the function’s arguments to be constant. So, the final result of using the `partial()`

function will print out an elegant, readable, and reusable code.

Before using the `partial()`

function, we must import it from the Functools library. Let’s see how we implement the function.

```
from functools import partial
```

As we have imported the `partial`

library using the above code, we can use the `partial`

command as below. Then we can call over the `partial()`

function as we want, and it outputs the function similar to the defined function along with a fixed value.

Below is the standardized `partial()`

function and its attributes.

```
partial(func, /, *args, **keywords)
```

The `partial`

function consists of three main attributes: function, arguments, and keywords.

`partial.func`

(function name) - A callable object or a function that returns the name and hexadecimal address of the parent function.`partial.args`

(positional arguments) - This attribute returns the pre-assigned arguments to the`partial()`

function.`partial.keyword`

(keyword arguments) - This attribute returns the pre-assigned keywords to the`partial()`

function.

Let’s define an example using the `partial()`

function and its attributes.

Full Code:

```
from functools import partial
# original function
def multiply(a, b):
return a * b
# partial function to multiply a as 2
multiplication1 = partial(multiply, 2)
print(multiplication1(4))
# partial function to multiply b as 7
multiplication2 = partial(multiply, b=7)
print(multiplication2(3))
# simple multiply function with two variables
print(multiply(5, 2))
# partial function with two values and multiply function
multiplication3 = partial(multiply, 2, 5)
print(multiplication3())
# defining some attributes in multiplication1, multiplication2 multiplication3
print("Function used in multiplication1 :", multiplication1.func)
print("Keywords for multiplication2 :", multiplication2.keywords)
print("Arguments for multiplication3 :", multiplication3.args)
```

Output:

At first, we imported the `partial()`

function from `functools`

and defined a function named `multiply()`

with two variables as `a`

and `b`

. This `multiply`

function multiplies two numbers `(a,b)`

together.

```
from functools import partial
def multiply(a, b):
return a * b
```

In the below code chunk, the `partial()`

function is called and outputs a function object `multiply()`

along with a fixed value of `2`

. Here, the `partial()`

function calls the `multiply()`

with `a`

as `2`

.

When printing, it assigns `4`

for `b`

and prints the result as `8`

.

```
multiplication1 = partial(multiply, 2)
print(multiplication1(4))
```

Here, when the `partial()`

function gets called, it prints out the `multiply()`

function and the value assigned for `b`

as `3.`

It has specified the value for the variable `b`

by skipping the parameter of the original function.

When printing, it has defined a value for `a`

as `3`

and displays the output as `21`

.

```
multiplication2 = partial(multiply, b=7)
print(multiplication2(3))
```

The `partial()`

function is not essential when calling the function with values for two variables. As usual, it takes `5`

for `a`

, `2`

for `b`

, and prints out the result as `10`

.

```
print(multiply(5, 2))
```

As the original function has two parameters when calling the `partial()`

function, it will not be an issue, and it takes `multiply()`

with `a`

as `2`

and `b`

as `5`

. Then, it displays the result as `10`

.

```
multiplication3 = partial(multiply, 2, 5)
print(multiplication3())
```

The below code chunk displays the function used in the function `multiplication1`

, keywords in `multiplication2`

, and arguments in `multiplication3`

, respectively. So, the function used in `multiplication1`

is `multiply()`

, and its hexadecimal value is `000001E523A6E4C0`

.

In `multiplication2`

, we have used `{'b': 7}`

as keywords while `2, 5`

are the arguments used in `multiplication3`

.

```
print("Function used in multiplication1 :", multiplication1.func)
print("Keywords for multiplication2 :", multiplication2.keywords)
print("Arguments for multiplication3 :", multiplication3.args)
```

## Conclusion

This article discussed the `partial()`

function of the `functools`

library. As you saw in the previous examples, using the `partial()`

function makes our code more readable, elegant, and fast.

If you find a function that freezes one or more arguments, the `partial()`

function will be the best for that situation.

**Migel Hewage Nimesha**

Nimesha is a Full-stack Software Engineer for more than five years, he loves technology, as technology has the power to solve our many problems within just a minute. He have been contributing to various projects over the last 5+ years and working with almost all the so-called 03 tiers(DB, M-Tier, and Client). Recently, he has started working with DevOps technologies such as Azure administration, Kubernetes, Terraform automation, and Bash scripting as well.